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       realpath - return the canonicalized absolute pathname


       #include <limits.h>
       #include <stdlib.h>

       char *realpath(const char *path, char *resolved_path);


       realpath  expands  all symbolic links and resolves references to '/./',
       '/../' and extra '/' characters in the null terminated string named  by
       path  and  stores  the canonicalized absolute pathname in the buffer of
       size PATH_MAX named by resolved_path.  The resulting path will have  no
       symbolic link, '/./' or '/../' components.


       If there is no error, it returns a pointer to the resolved_path.

       Otherwise  it  returns  a  NULL  pointer, and the contents of the array
       resolved_path are undefined.  The  global  variable  errno  is  set  to
       indicate the error.


       EACCES Read or search permission was denied for a component of the path

       EINVAL Either path or resolved_path is NULL. (In libc5 this would  just
              cause a segfault.)

       EIO    An I/O error occurred while reading from the file system.

       ELOOP  Too  many  symbolic  links  were  encountered in translating the

              A component of a path name exceeded NAME_MAX characters,  or  an
              entire path name exceeded PATH_MAX characters.

       ENOENT The named file does not exist.

              A component of the path prefix is not a directory.


       The libc4 and libc5 implementation contains a buffer overflow (fixed in
       libc-5.4.13).  Thus, suid programs like mount need a private version.

       The length  of  the  output  buffer  should  have  been  an  additional
       parameter,  especially  since  pathconf(3)  warns  that  the  result of
       pathconf() may be huge and unsuitable for mallocing memory.


       The realpath function first appeared in BSD 4.4,  contributed  by  Jan-
       Simon Pendry.  In Linux this function appears in libc 4.5.21.


       In  BSD  4.4 and Solaris the limit on the pathname length is MAXPATHLEN
       (found in <sys/param.h>). The SUSv2 prescribes PATH_MAX  and  NAME_MAX,
       as  found  in  <limits.h>  or  provided  by  the pathconf() function. A
       typical source fragment would be

              #ifdef PATH_MAX
                path_max = PATH_MAX;
                path_max = pathconf (path, _PC_PATH_MAX);
                if (path_max <= 0)
                  path_max = 4096;

       The BSD 4.4, Linux and SUSv2 versions always return  an  absolute  path
       name. Solaris may return a relative path name when the path argument is
       relative.  The prototype of realpath is given in  <unistd.h>  in  libc4
       and libc5, but in <stdlib.h> everywhere else.


       readlink(2), getcwd(3), pathconf(3), sysconf(3)

                                24 August 1999                     REALPATH(3)